\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)
\(\frac{B}{7}=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.4}\)
\(\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{15}-\frac{1}{28}\)
\(\frac{B}{7}=\frac{1}{2}-\frac{1}{28}\)
\(\frac{B}{7}=\frac{13}{28}\)
\(B=\frac{13}{28}.7=\frac{13}{4}\)
B=5/1.2+4/1.11+3/11.2+1/2.15+13/15.4
B/7=5/2.7+4/7.11+3/11.14+1/14.15+13/15.4
B/7=1/2-1/7+1/7-1/11+...+1/15-1/28
B/7=1/2-1/28
B/7=13/28
B=13/28.7=13/4
Câu trả lời của bạn Ho nguyen ở dong 2 là sai vì 13/15.4 phai chuyen thanh 13/15/28
Nguyễn Đình Tuấn Hưng sai rồi vì \(\frac{13}{15.28}\)chứ không phải \(\frac{13}{\frac{15}{28}}\)
B=\(\frac{5}{2.1}\)+\(\frac{4}{1.11}\)+\(\frac{3}{11.2}\)+\(\frac{1}{2.15}\)+\(\frac{13}{15.4}\) \(\frac{B}{5}\)=\(\frac{5}{2.5}\)+\(\frac{4}{5.11}\)+\(\frac{3}{11.10}\)+\(\frac{1}{10.15}\)+\(\frac{13}{15.20}\) \(\frac{B}{5}\)=\(\frac{1}{2}\)_\(\frac{1}{5}\)+\(\frac{1}{5}\)_\(\frac{1}{11}\)+\(\frac{1}{11}\)_\(\frac{1}{10}\)+\(\frac{1}{10}\)_\(\frac{1}{15}\)+\(\frac{1}{15}\)_\(\frac{1}{20}\) \(\frac{B}{5}\)=\(\frac{1}{2}\)_\(\frac{1}{20}\) \(\frac{B}{5}\)=\(\frac{10}{20}\)+ \(\left(-\frac{1}{20}\right)\) \(\frac{B}{5}\)=\(\frac{9}{20}\)
